This invention concerns with a vacuum evaporating apparatus for making thin films, particularly with a vacuum tube type furnace with electrode pins for heating wire and thermocouples.
In these days it has been increasingly requirement to make thin films of a metal, semiconductor, superconductor and the like on a substrate, not only in the electronics field but also in various other fields. For electronics in order to obtain high quality films molecular beam epitaxy (MBE) is one of the powerful methods using vacuum evaporating system. Even synthetic materials such as superlattices can be made by using atomic scale growth control.
Concerning depositing gas, elements or molecules evaporated from the source materials are widely used in a standard vacuum evaporating method. As a result of much progress in the chemical vapour deposition (CVD) method, metalorganic gas has been recently increasingly used for the vacuum evaporating method also, resulting in metal-organic molecular beam epitaxy (MOMBE). For this epitaxy the metal organic molecules should be cracked to be metal molecules and organic molecules before reaching the substrate. Thus, for example, a heated chamber to provide the metal organic molecule with sufficient energy for these molecule to be cracked, must be supplied in the system.
Hot wall epitaxy is a kind of MBE. Crystal film of III-V compound, an excellent infrared semiconductor laser device consisting of IV-VI compounds and II-VI compound semiconductor superlattices have been produced by means of this epitaxy. This hot-wall epitaxy is described in U.S. Pat. 4,662,981.
The epitaxial film growth is always carried out using a heated chamber (furnace) which contains some crucibles for source materials. The evaporated gas from the crucibles flows out to a substrate through the space surrounded by a hot wall. Photons from the hot wall, which is just below the substrate, radiate the growing film surface and make it possible to grow high quality films on the substrate because of giving energy and momentum to the surface atoms, and especially to the loosely bound unstable atoms on the substrate.
A part of the depositing gas flows out through a small gap in between the substrate holding plate and the open top of the hot wall tube. This blocks introduction of residual gas molecules such as O.sub.2 to the growing film surface, but sometimes induces such troubles as electrical shorts, the breaking of the heating wire, or contamination on the outer part of the hot wall furnace.
The aforementioned prior art hot wall epitaxy is carried out in a conventional technique by using a "hot-wall furnace" located in a vacuum evaporating apparatus as shown in FIG. 6.
Referring to FIG. 6, a prior art "hot-wall furnace" essentially consisting of a heating means 2 comprises a silica glass tube provided with a first recess 3 for holding a first material as a source to be evaporated, called an evaporation source material hereinafter, and a second recess 4 disposed coaxially below the first recess 3 for holding a second evaporation source material. There are also first and second heaters 5 and 6 located around the first and second recesses 3 and 4, respectively independently to control the temperatures of the corresponding recesses 3 and 4, and first and second thermocouples 7 and 8 for the respective heaters 5 and 6.
Within the heating means 2 is disposed a crucible vessel 11 provided with first and second crucibles 9 and 10 for accommodating the first and second evaporation source materials, respectively, as shown in FIG. 7, to form a thin film made of more than one kind of metal, non-metals or compounds on the substrate disposed above the heating furnace. The upper part of the crucible 9 acts as a hot wall.
With the conventional heating means 2 having the construction described above, the crucible vessel 11 can be easily exchanged, but the exchange of the heating means 2 in case of contamination thereof, or the interruption of the heater and the exchanges of the heating elements and the thermocouples attached to the heating means 2 can not easily be performed. For this reason, as one example, it will be pointed out that the thermocouples extending outwardly of the heating means 2 and make-up lead wires connected to the thermocouples are connected to the heating furnace. This wiring or connection makes it difficult to easily exchange the heating means and the like elements of the hot-wall furnace 1.
Lead connections make it difficult to easily exchange the hot-wall furnace 1 in case of the troubles mentioned above. These conventional vacuum evaporating apparatus or methods are not suitable for the mass production of the evaporated thin film, this being a significant problem in the conventional technique.